For many years, lithographic printing has utilized a process known as step and repeat photocomposing. In such a process, rows and columns of aligned images are prepared by stepping an image producing film transparency from position to position. In the past a difficulty was encountered in precisely locating the image producing film transparency in such a manner as to properly locate the various images. Also, in multi-color printing where several colored images are to be reproduced by stepping type of photocomposing, a problem was encountered in registering the film transparencies or the carriers bearing the film transparencies. The problems were at least partially solved by an invention described and claimed in U.S. Pat. No. 2,983,049. The apparatus there described has been highly successful for many years. Certain problems have persisted over the years even with the use of such apparatus. In the operation of the step and repeat apparatus of U.S. Pat. No. 2,983,049, a vacuum is drawn between the step and repeat board and the film transparency. Since the process is repeated many times during the work day, time is of the essence. Therefore, a need for improvement in cycling time has remained. Another problem has been encountered in the vacuum draw-down of the film transparency in which certain areas of the film transparency may be blocked. In other words, a small amount of air remains between the film transparency and the exposing material mounted on the step and repeat board. The lack of perfect vacuumizing creates some surface irregularity and thus the precise contact or exposure of the images to the material to which the images are being transferred.
In the present invention, an improvement was obtained in the rate at which draw-down may be obtained during vacuumizing, for example, improvement of as much as 20-50% over those encountered in the past. The present invention also serves to minimize or eliminate any loss of precise contact thus providing significant improvement in the precision of transferring of images.